More accurately, no. Nearly all gang-related shootings involve illegally obtained weapons. A little over half of killings related to spouse-on-spouse domestic violence involve legally obtained weapons, and about a third of those weapons were borrowed from a relative or friend. The majority of mass shootings involved legally obtained weapons, but not all were obtained by the shooter.
I forget the exact numbers. I saw the stats charted on a US gun-crime website. I didn't save the link, but it's ez to look it up.
Some US states require more in-depth background checks than others. some do not require them at all, and some actually prohibit them (
https://www.shrm.org/ResourcesAndTo...dates/Pages/state-laws-background-checks.aspx ). Some states require registering your firearms, some do not. Some allow open carry, some allow concealed carry. Some have long wait periods, some have short ones, some have no wait period.
All those things ^ depend on the type of gun, and that also varies from state to state, but not by much.
There is one constant - you can't buy or own or possess a gun if you've ever been charged with a felony. And I think that if you've ever been housed in a mental hospital, you can't own, buy, or possess a gun unless you have clearance from a mental health professional.
In any case, a) gun theft is too common, and, b) all 50 states agree you can't own a bazooka, missile-launcher, an armed tank, and most grenades.